EP-B-0 743 144 discloses a shaving head formed from a combination of an under cutter and an outer cutter. The outer cutter of the shaving head is constructed as a perforated foil and cooperates with an under cutter formed from a plurality of blades, with the cutting edges of the individual blades having a cutting angle of less than 90°. DE-C-44 23 503 discloses an under cutter for a shaving head on which the blades have a cutting edge angle of 90°.
Whether constructed as a rotary or an oscillatory system, the outer cutter and under cutter, being at least partly in direct contact with each other, cooperate. Shaving apparatus on which the under cutters are equipped with so-called 90° cutting edges are typically characterized by optimum skin protection, whereas under cutters with a cutting edge angle of less than 90° are typically characterized as having a somewhat better “stroking action” on account of the lower cutting forces. Dry shaving can be accompanied by skin irritations on account of interactions between the under cutter and the skin which arches into the shearing apertures of the outer cutter. When using cutting edges with a cutting angle of 90°, the skin can be urged undamaged back out of the shearing aperture of the outer cutter, but in the case of a sharp cutting edge with a small edge radius and a smaller cutting edge angle the skin may be injured or at least irritated. With so-called “sharp-edged” under cutters it is possible in principle to perform a more thorough shave because these cutters can also capture and shorten even the shortest hairs by incision.